1. Field of the Invention
The present invention relates to an exhaust gas purifying catalyst for effectively purifying carbon monoxides (CO), hydrocarbons (HC) and nitrogen oxides (NOx) contained in exhaust gas from an automotive engine.
2. Description of Background Art
Three-way catalysts for simultaneously purifying carbon monoxides (CO), hydrocarbons (HC) and nitrogen oxides (NOx) contained in the exhaust gas usually support noble metals such as platinum, rhodium and palladium, and are now in wide use as exhaust gas purifying catalysts. Of these noble metals supported in the exhaust gas purifying catalysts, rhodium exhibits excellent activity for oxidation and reduction and develops the excellent effect in purification of NOx in particular. For this reason, a variety of proposed exhaust gas purifying catalysts use rhodium as their essential component and support platinum or palladium in combination with the rhodium.
In the meantime, rhodium is expensive and there has been a strong industrial desire to produce an exhaust gas purifying catalyst that requires a smallest possible quantity of rhodium for effectively developing the equivalent effect.
It is the object of the present invention to provide an exhaust gas purifying catalyst that requires a smallest possible quantity of rhodium for effectively developing the activity to produce an excellent purifying performance economically.